Remove compiler/ast/endianness.h

Summary:
Remove `compiler/ast/endianness.h` because it has nothing to do with AST and only used in two places. Replace its uses with conditionally compiled calls to `__builtin_bswap64`. Another option is to move `endianness.h` outside of AST but it's probably an overkill considering that there are only two uses, three lines of code each.

While at it fix UBs due to invalid type conversion.

Reviewed By: Mizuchi

Differential Revision: D30883166

fbshipit-source-id: 024b0c09454057b732a36baa024e1de77fc8535c

thrift/compiler/ast/t_type.cc

@@ -23,7 +23,6 @@
 
 #include <openssl/sha.h>
 
-#include <thrift/compiler/ast/endianness.h>
 #include <thrift/compiler/ast/t_program.h>
 #include <thrift/compiler/ast/t_typedef.h>
 
@@ -60,19 +59,15 @@ const std::string& t_type::type_name(type t) {
 }
 
 uint64_t t_type::get_type_id() const {
-  // This union allows the conversion of the SHA char buffer to a 64bit uint
-  union {
-    uint64_t val;
-    unsigned char buf[SHA_DIGEST_LENGTH];
-  } u;
-
   std::string name = get_full_name();
-  SHA1(reinterpret_cast<const unsigned char*>(name.data()), name.size(), u.buf);
-  const auto hash =
-      apache::thrift::compiler::bswap_host_to_little_endian(u.val);
-  type tv = get_type_value();
-
-  return (hash & ~t_type::kTypeMask) | int(tv);
+  unsigned char buf[SHA_DIGEST_LENGTH] = {};
+  SHA1(reinterpret_cast<const unsigned char*>(name.data()), name.size(), buf);
+  uint64_t hash = 0;
+  std::memcpy(&hash, &buf, sizeof(hash));
+#if !defined(_WIN32) && __BYTE_ORDER__ != __ORDER_LITTLE_ENDIAN__
+  hash = __builtin_bswap64(hash);
+#endif
+  return (hash & ~t_type::kTypeMask) | static_cast<int>(get_type_value());
 }
 
 std::string t_type::get_scoped_name() const {

thrift/compiler/generate/t_concat_generator.cc

@@ -22,8 +22,6 @@
 
 #include <openssl/sha.h>
 
-#include <thrift/compiler/ast/endianness.h>
-
 #include <thrift/compiler/generate/t_generator.h>
 
 using namespace std;
@@ -152,17 +150,17 @@ std::string t_concat_generator::generate_structural_id(
   std::string hashable_keys_list = ss.str();
 
   // Hash the string and generate a portable hash number.
-  union {
-    uint64_t val;
-    unsigned char buf[SHA_DIGEST_LENGTH];
-  } u;
+  unsigned char buf[SHA_DIGEST_LENGTH] = {};
   SHA1(
       reinterpret_cast<const unsigned char*>(hashable_keys_list.data()),
       hashable_keys_list.size(),
-      u.buf);
-  const uint64_t hash =
-      (apache::thrift::compiler::bswap_host_to_little_endian(u.val) &
-       0x7FFFFFFFFFFFFFFFull); // 63 bits
+      buf);
+  uint64_t hash = 0;
+  std::memcpy(&hash, &buf, sizeof(hash));
+#if !defined(_WIN32) && __BYTE_ORDER__ != __ORDER_LITTLE_ENDIAN__
+  hash = __builtin_bswap64(hash);
+#endif
+  hash &= 0x7FFFFFFFFFFFFFFFull; // 63 bits
 
   // Generate a readable number.
   char structural_id[21];